The Pilot Feasibility Studies Program, known as the O'Brien Fellows. Is designed as an efficient, effective and exciting framework in which Investigators new to the potential of fluorescence microscopy can begin to realize its transformational potential for their research. We propose a continuation of the O'Brien Fellows Program as the Pilot Feasibility Studies Program for the Center, replacing the conventional pilot grant program used In the original application and the last renewal of the Center. Up to 10 O'Brien Fellows will be selected In each of Years 1-5 of this award. Fellows will stay in Indianapolis in on-campus furnished apartments or local hotels for up to four weeks. The fellowship will help defray the cost of return travel to Indianapolis, apartment rental/hotel stay, supplies and consumables, animal procurement and housing and microscope time. Each fellow will be assigned to a liaison who is a senior investigator associated with the Center. The fellow will be provided with extensive training on the multiphoton microscope systems, and in other related techniques relevant to the proposed project